This invention relates to an improvement in the active flight control of an air vehicle, and more particularly, but not by way of limitation, to a split span fin tail control arrangement whereby inner and outer spans of each fin are independently operable to provide yaw, roll, and pitch control for an air vehicle in flight.
The control of air vehicles in flight, such as manned air vehicles, is provided by control surfaces located in the tail area of the vehicle. These controlled surfaces include the horizontal tail area which includes a horizontally disposed elevator of which approximately 60% is fixed with remainder being movable about an horizontal axis. In steady flight the function of the horizontal elevator is to balance or trim the air vehicle to ensure the resultant of all the air forces on the vehicle pass through its center of gravity. The trim control provided by the horizontal elevator provides longitudinal or pitch control of the air vehicle.
The vertical tail portion includes vertical stabilizing and controlling surfaces that are provided by a fixed fin and a movable rudder. These surfaces perform the same function as the rudder in a boat. The fixed fin provides directional stability; i.e., it provides a means to "yaw" the air vehicle and change the direction of flight and it is used to trim the air vehicle for straight flight. The control surfaces of the horizontal and vertical tail surfaces cooperate to control the roll of the vehicle in flight.
The term "air vehicles" is also considered to include unmanned air vehicles with which the present invention may be employed to particular advantage. Unmanned air vehicles may be used for missions such as the delivery of a payload in which the mission requirements necessitate guidance of the vehicle in flight to a precise target. Unmanned air vehicles may also be used for such tasks as day/night reconnaissance, surveillance and target acquisition systems which use the unmanned air vehicles as sensor platforms. The propulsion for an unmanned air vehicle may be provided by a rocket motor, gas turbine engine, or by a reciprocating internal combustion engine. Such unmanned air vehicles may be vertically launched or be launched in flight from a manned air vehicle.
Generally speaking, the most common means to provide longitudinal and directional stability for an unmanned air vehicle included a minimum of three active control fins and often four such fins. As opposed to the horizontal and vertical tail control surfaces commonly used for manned air vehicles as described above, the active control surfaces of an unmanned air vehicle provides for controllable movement of the entire fin about an axis normal to the center line of the air vehicle.